“阿伏伽德罗常数”学习困境分析与对策探讨

探索"阿伏伽德罗常数"中"规定"表述背后隐藏的玄机:0.012 kg~(12)C中含有多少原子;"阿伏伽德罗常数"为什么选择~(12)C作为基准;"阿伏伽德罗常数"的数值如何确定等。得出启示,教师对于"规定"表述应当利用学生的原有经验,发挥学生的自主性;挖掘科学史资源,揭示知识的修正性;结合实验过程,突出实验的重要意义。     

关于“阿伏伽德罗常数”的历史考量

从基本物理常数这个视角来看阿伏伽德罗常数会更易理解。最早测出阿伏伽德罗常数的人是法国科学家佩兰。阿伏伽德罗常数的测定历史长达百年,至今仍在继续。"阿伏伽德罗常数"与"物质的量""摩尔"概念具有相同的历史源头,但是在不同学科领域发展着,最后又殊途同归。     

学生园地阿伏伽德罗常数与气体常数测定实验的改进

对阿伏伽德罗常数与气体常数测定实验进行了改进:将原实验中测阴极铜片增重改为测阳极铜片的减重;改变电解液的性质,引入EDTA络合铜离子;用相对更环保的锌片代替铜片等。经过反复实验,最终得到了较优化的实验方案。     

基于手持技术的阿伏伽德罗常数测定

借助手持技术通过电镀法和双液原电池法实验测定阿伏伽德罗常数，进而得出一种新的近似测定阿伏伽德罗常数的方法，并作为教材实验的有益补充，帮助学生理解概念，切实感受化学定量实验的魅力。     

阿佛加德罗常数测定实验中胶头滴管的代用

现行六年制重点中学高中《化学》第一册第163页上,用单分子膜法来测定阿佛加德罗常数的学生实验。为减小实验误差,实验中所用的胶头滴管,必须“尖嘴拉得很细”。     

对高考化学试题中部分错误的分析及修改建议

对高考化学试题中出现的小错误,进行了错因分析,并提出了修改建议,其中包括正方形构型的键角,阿伏伽德罗常数的使用,氯化铝的结构,喷泉实验等。     

物质的量和摩尔

叙述了两种物质的量的比率的测量方法。介绍了物质的量的SI单位——摩尔。定义了涉及物质的量的一些量,其中包括摩尔质量、一般的摩尔量、阿伏伽德罗常数、摩尔气体常数及法拉第常数等。对物质的量及其单位摩尔的概念作了有关历史的叙述。     

物质的量和摩尔

叙述了两种物质的量的比率的测量方法。介绍了特的量的ＳＩ单位－摩尔。定义了涉及物质的理的一些量，其中包括摩尔质量、一般的摩尔量、阿伏伽德罗常数、摩尔气体常数及法拉第常数等。对物质的量及其单位摩尔的概念作了有关历史的叙述。     

摩尔新定义和准确测定的阿伏伽德罗常数

针对2019年国际SI单位新标准的实施,依据文献对阿伏伽德罗常数和摩尔物质量原理进行了简短的历史回顾。着重于摩尔新定义的概念和准确测定阿伏伽德罗常数的描述,突出了原子量精密测量技术、纳米量级精密测量技术以及材料制备和表征技术的发展。相对而言,摩尔新定义更能体现科学方法和科学思维同化学知识的关系,将会对无机化学、分析化学、物理化学等课程教学引起巨大的冲击波,并且会波及到每个化学专业本科生。本文内容可为提高本科生的科研思维和科研素质提供借鉴。     

连续重整催化剂铂中心可接近性研究

在AutoChem II 2920化学吸附仪上,探索以环己烷、苯、甲苯、正庚烷和甲基环戊烷为新有机探针分子表征重整催化剂中Pt的可接近度．通过脉冲实验表明,单铂催化剂在合适条件下可以用环己烷、苯和正庚烷表征出全部金属活性中心;双金属催化剂用苯为探针分子在350℃可以表征全部的金属活性中心,用环己烷作为探针分子在100℃或者正庚烷作为探针分子在170℃可以表征双金属催化剂中的非合金Pt．     

二氧化碳和丙烯直接合成甲基丙烯酸的NiPMo/TiO2催化剂的研究

用溶胶-凝胶法以磷钼酸(MPA)的镍盐溶液水解钛酸四丁酯制备了NiPMo/TiO2催化剂.使用ICP、 XRD、 TG-DTA、 IR、 TPD-MS和微反应技术研究了催化剂的化学组成、热稳定性、化学吸附性质和催化反应性能.杂多钼酸盐与TiO2通过O2-在TiO2表面发生了键合.在623 K下,杂多阴离子仍保持原有的Keggin结构.CO2在Lewis酸位Ni(Ⅱ)和Lewis碱位Ni-O-Mo的桥氧协同作用下生成CO2卧式吸附态Ni(Ⅱ)←O-(CO)←(O--Ni).丙烯有多种吸附态在催化剂上吸附.在563 K、 1 MPa和空速1500 h-1的反应条件下,丙烯的摩尔转化率为3.2%,产物MAA选择性为95%.     

Synthesis of 1-benzyloxypyrazin-2(1H)-one derivatives

Different approaches for the synthesis of 1-benzyloxypyrazin-2(1H)-one derivatives from simple amino acids have been investigated. A library of 33 precursors for the preparation of N-hydroxy pyrazinones was obtained in moderate to good yields.     

A general and convenient synthesis of 4-(tosylmethyl)semicarbazones and their use in amidoalkylation of hydrogen,heteroatom, and carbon nucleophiles

A general synthesis of previously unknown semicarbazone-based α-amidoalkylating reagents, 4-(tosylmethyl)semicarbazones, has been developed. The synthesis involved three-component condensation of semicarbazones of aliphatic or aromatic aldehydes with the same or other aldehydes and p-toluenesulfinic acid. The scope and limitations of this reaction were investigated. The compounds obtained were demonstrated to be an efficient α-(4-semicarbazono)alkylating agents. They were reacted with H- (sodium borohydride), O- (sodium methylate), S- (sodium phenylthiolate), N- (pyrrolidine, sodium succinimide), P- (trialkyl phosphites), and C-nucleophiles (sodium diethyl malonate) to give the corresponding products of the tosyl group substitution, 4-substituted semicarbazones, including analogues of nitrofurazone. Among the prepared compounds tested in vitro for antibacterial and antifungal activity, three nitrofuryl-containing semicarbazones exhibited high biological activities with minimum inhibitory concentration (MIC) values of 8–32 μg/mL.     

Synthesis of novel chiral bidentate hydroxyalkyl-N-heterocyclic carbene ligands and their application in palladium-catalyzed Mizoroki–Heck couplings and asymmetric addition of diethylzinc to benzaldehyde

A small library of new chiral bidentate hydroxyalkyl-imidazolium salts 1 is conveniently synthesized on multi-gram scale from inexpensive and commercially available chiral pool amino acids. The corresponding carbenes, generated by deprotonation of imidazolium salts 1, in combination with palladium(II) chloride were tested in the Mizoroki–Heck coupling reaction. The most significant results in terms of yields and reactivities were achieved with low catalyst loading. The catalytic activities of these imidazolium salts were also investigated in the asymmetric addition of diethylzinc to benzaldehyde. The use of MgO nanoparticles as an additive in conjunction with these ligands played a crucial role in increasing the efficiency of these reactions.     

Toward new camptothecins. Part 6: Synthesis of crucial ketones and their use in Friedländer reaction

In the context of the preparation of camptothecin and luotonin A analogs, the synthesis of some key keto-precursors and their use in Friedländer condensation are described. This paper also focuses on the stability of these keto intermediates and emphasizes the major differences between indolizinones and pyrroloquinazolinones series. Noteworthy is also the report of some original structures isolated as by-products of some experiments.     

α-Amino acid derived enaminones and their application in the synthesis of N-protected methyl 5-substituted-4-hydroxypyrrole-3-carboxylates and other heterocycles

A new and simple synthesis of novel N-protected methyl 5-substituted-4-hydroxypyrrole-3-carboxylates, which exist in equilibrium with their 4-oxo tautomers, has been developed in two steps starting from N-protected α-amino acids. The key intermediates are enaminones, which can also be isolated, characterized, and used for the construction of other functionalized heterocycles, before they spontaneously decompose to pyrrole products. 4-Hydroxypyrroles are prone to partial aerial oxidation but can be efficiently alkylated or reduced to stable polysubstituted pyrrolidine derivatives.     

Specific intramolecular aromatic CH insertion of diazosulfonamides

The chemoselectivity in the intramolecular CH insertion of various diazosulfonamides has been experimentally studied. The results reveal that the aliphatic 1,4-, 1,5-, or 1,6-C(sp³)?H insertions of diazosulfonamides are not accessible, while the aromatic 1,5-C(sp²)?H insertion can be realized specifically by adjusting the diazo-adjacent group. In addition, the general chemoselectivities in the intramolecular CH insertions of diazosulfonyl compounds are summarized. Generally, diazosulfones undergo both aromatic 1,5-C(sp²)?H and aliphatic 1,5- and 1,6-C(sp³)?H insertions, while diazosulfonates undergo aliphatic 1,5- and 1,6-C(sp³)?H insertions. However, diazosulfonamides only undergo aromatic 1,5-C(sp²)?H insertion.     

CoFe2O4自形成磁性液体场致结构化对磁化的影响

The Langevin paramagnetic theory can’t describe the relation between magnetization of ferrofluids and applied magnetic field. The structuralization of ferrofluids, which is considered the main influence factor of the magnetization, is regarded. The part of magnetization works is deposited when the structure is forming. This action influences the magnetization of ferrofluids directly or indirectly. On the base of the “compressing” model, the Langevin function that usually describes the magnetization of ferrofluid is modified, and a well-fitted curve is obtained. An equation of the relation between the equivalent volume fraction after being “compressed” and the intensity of magnetic field is discovered, which approximately describes the process of magnetization. The relation between the approximate initial susceptibility and the volume fraction can be obtained from modified formula.     

Microwave-assisted copper-catalyzed stereoselective ring expansion of three-membered heterocycles with α-diazo-β-dicarbonyl compounds

Microwave-assisted copper-catalyzed ring expansions of three-membered heterocycles with α-diazo-β-dicarbonyl compounds were investigated. Thiiranes generated 3-acyl-5,6-dihydro-1,4-oxathiines in the presence of copper sulfate and trans-3-acyl-5,6-dihydro-1,4-oxathiines as stereospecific products for 1,2-disubstituted cis-thiiranes through an intramolecular S_N2 process. Oxiranes gave rise to 2-acyl-5,6-dihydro-1,4-dioxines under the catalysis of copper hexafluoroacetylacetonate and cis-3-acyl-5,6-dihydro-1,4-dioxines as stereospecific products for 1,2-disubstituted cis-oxiranes via an intimate ion-pair mechanism. The current method provides a direct and simple strategy in efficient preparation of 3-acyl-5,6-dihydro-1,4-oxathiines and 2-acyl-5,6-dihydro-1,4-dioxines, important agents in medicinal and agricultural chemistry, from readily available thiiranes and oxiranes, respectively.     

KMnO4-mediated oxidative CN bond cleavage of tertiary amines: Synthesis of amides and sulfonamides

KMnO₄-mediated oxidative CN bond cleavage of tertiary amines producing secondary amine was introduced, which was trapped by electrophiles (acyl chloride and sulfonyl chloride) to form amides and sulfonamides. The reaction could take place at mild condition, tolerating a wide range of function groups and affording products in moderate to excellent yields.